1. Field of the Invention
The present invention relates to Coriolis gyroscopes. More particularly, the invention pertains to a method for measurement of accelerations with a rotation rate Coriolis gyro, and to a Coriolis gyro suitable for such purpose.
2. Description of the Prior Art
Coriolis gyros (also referred to as “vibration gyros”) are increasingly employed for navigation. Such devices include a mass system that is caused to oscillate. The mass system generally has a large number of oscillation modes, initially independent of one another. A specific oscillation mode of the mass system is artificially excited to operate the Coriolis gyro. Such mode is referred to in the following text as the “excitation oscillation”.
Coriolis forces occur that draw energy from the excitation oscillation of the mass system when the Coriolis gyro is rotated and transmit a further oscillation mode of the mass system (referred to below as the “read oscillation”). The read oscillation is tapped off to determine rotations of the Coriolis gyro, and a corresponding read signal is investigated to determine whether any changes have occurred in the amplitude of the read oscillation which represent a measure of rotation of the Coriolis gyro.
Coriolis gyros may comprise either an open-loop or a closed-loop system. In a closed-loop system, the amplitude of the read oscillation is continuously reset to a fixed value (preferably zero) via respective control loops, and the resetting forces measured.
The mass system of the Coriolis gyro (referred to below as the “resonator”) may be of widely differing designs. For example, it is possible to use an integral mass system. Alternatively, it is possible to split the mass system into separate oscillators coupled to one another via a spring system and capable of movements relative to one another. High dimensional accuracies can be achieved, particularly with linear double-oscillator systems that comprise a coupled system of two linear oscillators. In double-oscillator systems, the spring system that couples the linear oscillators to one another is, in general, designed so that the two linear oscillators can be caused to oscillate along a first oscillation axis, with the second oscillator additionally oscillating along a second oscillation axis at right angles to the first oscillation axis. In such case, the movements of the second oscillator along the second oscillation axis can be regarded as a read oscillation while those of the first and second oscillators along the first oscillation axis can be regarded as an excitation oscillation.
Linear double-oscillator systems have the disadvantage that the oscillations of the two linear oscillators along the first oscillation axis can cause vibrations or reflections in the gyro frame. (The “gyro frame” should be understood to be a mechanical, non-oscillating structure in which the oscillators are “embedded”, e.g. a non-oscillating part of a silicon wafer.) The vibrations or reflections in the gyro frame can, in turn, lead to disturbances (e.g. damping effects) to oscillator movements. For example, the oscillations of the first and second linear oscillators along the first oscillation axis can be disturbed by both external vibrations and accelerations which act along the first oscillation axis. Analogously, external vibrations and accelerations acting in the direction of the second oscillation axis can disturb the oscillations of the second linear oscillator along that oscillation axis to corrupt the measured rotation rate—in precisely the same way as all of the other disturbance influences mentioned.